ToBE #13 : How are they related?

This is a story of three couples.
First, there was H1 who was married to W1. (H for Husband, W for Wife)
They had children H1W1.Boy and H1W1.Girl.

Also, there was H2 who was married to W2.
They had children H2W2.Boy and H2W2.Girl.

At this point, there is no relationship between the adults other than that of husband and wife.
Q : How are H1W1.Boy and H2W2.Boy related?
A : They are not related as their parents are complete strangers to each other.

For some unknown reason, the two couples split and H1 married W2. So far, they have no children.
At this point,
Q : How are H1W1.Boy and H2W2.Boy related?
A : They are now step-brothers. They do not have any common parent. However, a biological parent of H1W1.Boy is married to a biological parent of H2W2.Boy. Likewise, H1W1.Girl and H2W2.Girl are step-sisters.

Eventually, H1 and W2 had children, H1W2.Boy and H1W2.Girl.
Q1 : How is H1W2.Girl related to H1W1.Girl?
A : They are not sisters, because their mothers are different. They have one common parent, H1. They are half-sisters.

Q2 : How is H1W2.Girl related to H2W2.Girl?
A : Again, they are half-sisters.

______________________________________________________________